- What happened: Researchers at China's Harbin Institute of Technology and the Institute of Metal Research, Chinese Academy of Sciences, 3D-printed cement-based electrodes in an interdigitated (comb-shaped) pattern. The result is a prototype supercapacitor that stores electricity while also bearing structural loads.
- Why it matters: Because the electrodes are interleaved, the distance ions must travel does not grow easily even when the component is made thicker. This addresses one of the challenges of building energy storage into construction materials themselves.
- What to watch next: Compressive strength reached 23 MPa, but storage performance dropped sharply at −18°C. Before practical use, the design needs to be tested for durability under repeated charge-discharge cycles while under load, and for resistance to freezing and drying.
Researchers at China's Harbin Institute of Technology and the Institute of Metal Research, Chinese Academy of Sciences, 3D-printed cement-based electrodes in a comb-shaped pattern. They built a prototype supercapacitor that stores electricity while also serving as a load-bearing structural material.
The study was publicized by the American Chemical Society (ACS) on October 1. The samples showed a compressive strength of 23 MPa, and the team also connected three devices to light a small LED.
Research into giving cement and concrete themselves the ability to store energy has been under way for some time. What distinguishes this work is that the electrode layout is designed to tackle a known problem: making a component thicker lengthens the distance ions must travel, which lowers storage performance.
To build energy storage into structural elements such as walls and floors, rather than placing it separately from the building, a single material has to deliver not only storage capacity but also strength and moisture management.
The peer-reviewed paper, by Haiping Wu, Jing Zhong and Wencai Ren, was published online in ACS Nano on August 17. The ACS announcement on October 1 presented the findings to a general audience.
A comb-shaped structure that keeps ion travel distance short even in thicker parts
The team mixed carbon nanotubes, carbon black and cement to make an electrode material that can be extruded from a 3D printer nozzle.
This material is printed in a pattern in which the teeth of two combs interlock in alternation. The two electrodes do not touch; the space between them is filled with a cement-based separator, forming a single integrated structure.
Electrons move through the conductive pathways created by the carbon materials, while ions move between the electrodes through a solution of water and ions held in the pores of the cement-based material.
Combining a pathway for electrons with a pathway for ions in this way, the supercapacitor stores charge at the interface between electrode and electrolyte.
The cement itself does not generate electricity. Power obtained from sources such as solar generation is fed in from outside to charge it, then drawn out when needed.
In conventional stacked structures, a separator is sandwiched between two electrodes, so ions travel mainly through the thickness of the component.
As a result, making the electrodes thicker to increase storage also lengthens the ion travel distance, making it harder to use the interior fully.
In the new comb-shaped structure, ions move horizontally between the alternating electrodes.
This makes it easier to keep the ion travel distance between electrodes short even when the component itself is thicker. A key feature is that component thickness and ion travel distance can be designed fairly independently of each other.
In the samples described in the supplementary materials, the electrode teeth were 3 mm wide and 3 mm high, with a 5 mm gap between adjacent teeth.
By making both the electrodes and the separator from cement-based materials and integrating them, the design also aims to reduce delamination at boundaries where different components would otherwise be bonded together.
The novelty lies in designing not just the material mix but also the charge pathways and the load-bearing structure at the same time.
What area is the "22.52 μWh/cm²" figure based on?
The following performance has been reported for the team's optimized sample.
| Metric | Reported value / conditions |
|---|---|
| Areal capacitance | 162.14 mF/cm², measured at a current density of 0.46 mA/cm² |
| Areal energy density | 22.52 μWh/cm² |
| Areal power density | 0.49 mW/cm² |
| Operating voltage | 1.0 V |
| Compressive strength | 23.00 MPa |
Capacitance indicates how much charge can be stored, energy density how much energy can be extracted, and power density how quickly that energy can be delivered.
These are measurements for the samples the team built, not the storage performance of an entire building.
ACS says a compressive strength of 23 MPa is comparable to commercial concrete used for floor slabs and stairs. However, this comparison alone does not establish that the material can be used as-is as a building material.
There is another important caveat when reading the storage figures.
In Figure S18 of the published supplementary materials, the projected area of the printed electrode portion is labeled A, and the area of the whole device including the separator is labeled B.
In Section 1.4, which explains the calculation method, areal capacitance and similar values are calculated by dividing by the projected area of the electrodes.
In other words, the 22.52 μWh/cm² value is not based on the surface area of a wall or of the whole device.
A simple unit conversion gives:
22.52 μWh/cm² = 0.2252 Wh/m²
This is only the result of multiplying by 10,000 cm² per m² and converting μWh to Wh. It is not the result of building and measuring a large 1 m² device.
Nor does it mean that a whole component, including the non-electrode portions, can store 0.2252 Wh per square meter.
To estimate the storage of an actual wall or floor, one would need to evaluate it including the proportion of the component occupied by electrodes, their arrangement, and the thickness.
Multiplying this figure by a house's wall area would not give the storage capacity of the whole house.
MIT's storage concrete aims to solve a different problem
Among research on giving cement and concrete energy storage capability, MIT's conductive carbon concrete "ec³" is also well known.
In research MIT announced on October 1, 2025, improvements to the electrolyte and manufacturing method yielded a reported storage capacity of more than 2 kWh per cubic meter in a configuration using an organic electrolyte.
In MIT's work, the method changed from soaking hardened electrodes in electrolyte afterward to adding the electrolyte at the stage of mixing the concrete.
This reduced the need to wait for electrolyte to permeate the material, making thicker electrodes easier to produce.
The especially high performance came from an organic electrolyte combining a quaternary ammonium salt with acetonitrile.
In contrast, what the present study mainly changed is not the electrolyte itself but the shape and layout of the electrodes.
By integrating comb-shaped electrodes with the separator, it seeks to keep the distance ions travel short even when the component is thicker.
In short, the MIT study and this one are tackling different challenges in scaling up structural energy storage materials.
MIT's 2 kWh/m³ is a volume-based value, whereas the 22.52 μWh/cm² here is based on the projected area of the electrodes.
Because the sample structures and electrolytes also differ, the two cannot simply be placed side by side to say which has higher storage performance.
A more useful way to compare them is that MIT addresses the problem of getting electrolyte throughout thick material, while this study addresses the problem of creating ion pathways that are less affected by thickness.
Storage performance drops sharply at −18°C
In this supercapacitor, water and electrolyte contained in the cement's internal pores act as the pathway for ions.
Therefore, if temperature changes the state of the water in the pores, storage performance is affected.
Figure S13 of the supplementary materials shows performance at different temperatures, using capacitance measured at 25°C as the baseline.
The approximate values read from the figure are as follows.
| Measurement temperature | Capacitance relative to 25°C |
|---|---|
| 40°C | about 112% |
| 25°C | 100% |
| 5°C | about 92% |
| −18°C | about 8% |
At around 5°C there was no major drop, but at −18°C capacitance fell sharply.
The team cites as causes, among others, partial freezing of the solution in the pores, which reduced the liquid portion through which ions can move.
Even if the comb structure shortens ion travel distances, storage performance is greatly limited if the pathway itself freezes and ions can barely move.
The increase in capacitance at 40°C also does not mean the material is "heat resistant."
In the short term, higher temperature can make ions move more easily, but if hot, dry conditions persist, evaporation could change the state of the electrolyte in the pores.
The study did not conduct long-term tests under controlled humidity or examine long-term environmental degradation.
For real building materials, the problem is not only cold but also repeated drying and wetting, and freezing and thawing.
The team also points out that freeze-thaw cycles can create pressure and localized stress inside the pores, potentially leading to fine cracks and interface damage.
Such changes could affect both electrical resistance and mechanical strength, but long-term durability cannot be judged from this short-term temperature test alone.
Lighting an LED is one thing; powering a building is another
In the demonstration ACS described, three devices made on the same board were wired together to light a small LED.
The team lists emergency lighting and self-powered sensors as possible future uses.
However, this was not an experiment in supplying power to a house or an entire building.
Supercapacitors generally store less energy than batteries but can be charged and discharged quickly and used repeatedly.
Jing Zhong said in the ACS announcement that if the devices can be charged often enough from renewable sources such as solar, repeated charge-discharge cycles could potentially cover some power demand.
For now, then, the more plausible uses are powering low-consumption devices such as frequently charged sensors and lighting, rather than directly replacing large-capacity batteries.
For practical use as a building material, it is not enough to satisfy electrical performance and structural performance separately.
Even if an antifreeze electrolyte or moisture-retaining sealing is introduced, sufficient ionic conductivity and mechanical strength must be maintained.
The team names salts and gel electrolytes compatible with cement, and protective coatings, as future candidates.
The next key test is whether storage performance and structural strength can both be maintained under repeated charging and discharging while under load, and even after repeated freeze-thaw and dry-wet cycles.
If that can be confirmed, applications such as giving walls and floors themselves storage capability to power nearby sensors and lighting could be considered under conditions closer to real architectural design.